The present invention relates to machines for forming and/or processing webs of fibrous material, especially to papermaking machines. More particularly, the invention relates to improvements in rotary cylinders which can be utilized in such machines for conversion of a suspension of fibers into a paper or cardboard web, for guidance of the web and/or for transport of the web to further processing stations. Still more particularly, the invention relates to improvements in rotary cylinders which can be used with advantage in wire sections of papermaking or like machines.
A papermaking machine utilizes a host of rotary components, such as cylinders or rollers having uninterrupted peripheral surfaces, cylinders or rollers whose shells are foraminous (these include so-called egoutteurs or dandy rollers, sieves and others) and which serve for evacuation or expulsion of liquid from paper furnish or from a wet paper or cardboard web, several guide rolls, tensioning rolls and regulating rolls, as well as one or more wires, felts and/or nonpermeable sheets and foils.
Liquid-permeable felts, sieves and analogous components play a very important role in the manufacture of paper or cardboard webs because they allow for efficient expulsion of liquid from the paper furnish and/or moist web, either by gravity, by the application of mechanical pressure and/or by establishing a pressure differential between the opposite sides of the liquid-permeable components. Moreover, the application of higher pressure to one side and/or the application of lower pressure to the other side of a web renders it possible to conveniently transfer the web from a first component onto a second component or vice versa. For example, a rotary forming cylinder can attract the filaments of paper furnish as they issue from the slice of a head box or to attract a web which is transported by a wire or felt. Inversely, a cylinder wherein the pressure exceeds atmospheric pressure can be used to effect the transfer of a web from the periphery of the cylinder onto a wire or felt. A further important advantage of foraminous cylinders is that the force with which a wet web of artificial and/or natural fibers adheres thereto is much less pronounced than the adhesion of such web to a cylinder having an uninterrupted (non-permeable) peripheral surface. This facilitates the transfer of webs from foraminous cylinders to further transporting means which convey the web to successive processing stations.
All presently known foraminous cylinders for the formation, guidance and/or transport of paper webs or the like exhibit a number of serious drawbacks. For example, the shell of an egoutteur or a sieve must be supported from within by a complex, bulky and highly expensive core which is machined with a view to allow for evacuation of liquid therethrough. Since the core is heavy and bulky, it is likely to run out of round, to bend, to vibrate and/or to produce other undesirable effects. Furthermore, and since the core must exhibit a substantial strength, it cannot be designed to permit for practically unobstructed flow of that liquid which is free to pass through the permeable shell of the cylinder; therefore, the surplus of liquid (i.e., that quantity of liquid which is free to pass through the shell but is intercepted by the core) is likely to be sprayed onto the web and to adversely affect the appearance and/or other characteristics of the finished product. Still further, foreign matter which accumulates between the ribs of the core and the shell is likely to contaminate the shell and hence the web; such contaminants also affect the appearance and/or other qualities of the ultimate product.
The cleaning of cores in such cylinders is a difficult procedure, mainly because the cores cannot be cleaned from within, e.g., by jets of water or another cleaning fluid. Therefore, the cleaning of egoutteurs and analogous foraminous cylindrical components during operation of a papermaking machine is a problem which still awaits a satisfactory solution. Such components are cleaned periodically when the machine is at a standstill. This results in significant reduction of the output of the machine.
The cleaning of foraminous components in the form of elongated endless wires or felts is somewhat simpler, i.e., such components can be cleaned by directing jets of cleaning fluid against the internal surface of the wire or felt. However, the outlay for the cleaning equipment and the space requirements of such equipment are very high. As a rule, the wire or felt must be trained over several (at least three or four) rotary elements in the form of guide rolls, tensioning rolls, regulating rolls and others. The rolls must be mounted in a heavy and bulky frame, and the sieve or felt must be mounted for movement to and from the operative position.